I remember a joke about that, and maybe I'll post in in the joke forum. Nah, I'll pst it right here:

These 2 guys were riding on one horse for a few hours and they came upon a lake, so they stopped to let the horse take a drink. the horse went right up to the water, but would not drink. One guy says to the other "I know what to do, I'll put his face in the water, you suck on his butt to pull the water in". The second guy stupidly does this, and then says to the other guy "hold his head up higher, I'm only getting mud"